1. Field of the Invention
The present invention relates to a semiconductor package in particular, to a semiconductor package that is small and thin and that is suitable for a card type external storage medium or the like.
2. Description of the Related Art
A memory card that accommodates a semiconductor package having a memory function has a limited size (length, width, and thickness). Thus, the semiconductor package that has a memory function and the like should be thinly and compactly constructed so that it almost conforms with the outer shape of a semiconductor chip.
To satisfy such thin construction (for example, requirement of a space of 1 mm or less), TAB (Tape Automated Bonding) method, flip-chip mounting method, COB (Chip on Board) method, and so forth are known. FIGS. 1 and 2 show an example of a thin type package. Referring to FIGS. 1 and 2, a semiconductor chip 1 is mounted on a first main surface of a circuit board 2. External connecting terminals 4 are connected to a second main surface of the circuit board 2 via through-holes 3. A region on which the semiconductor chip 1 is mounted is sealed with a molded resin layer 5. Alternatively, the peripheral portion of the semiconductor chip 1 is sealed with a potting resin layer 5'. In FIG. 1, reference numeral 4a represents a bonding layer of the semiconductor chip 1 and reference numeral 6 represents bonding wires. In FIG. 2, reference numeral 1a represents bumps of the semiconductor chip 1.
In the construction of such a thin type package, as shown in FIG. 3, the external connecting terminals 4 are formed on the second main surface of the circuit board 2 with equal pitches in X and Y directions in a rectangular shape. The circuit board 2 has a wiring circuit that includes a connecting portion on the first main surface. Aluminum oxide, aluminum nitride, glass fiber reinforced epoxy resin, or the like is used as an insulator of the circuit board 2.
When one surface of the circuit board is sealed, the resultant semiconductor package can be more thinly constructed than the conventional molded plastic package (with a thickness of 1.0 to 1.2 mm). In consideration of the feature of thin construction, the thickness of the circuit board 2 is reduced to as small as 0.1 to 0.2 mm. However, as the thickness of the circuit board 2 is reduced, it tends to be deformed by a mechanical external stress (such as bending force and twisting force). Thus, in this case, the mounted semiconductor chip 1 tends to be damaged.
When a plurality of semiconductor chips are mounted, the size of the semiconductor chip 1 is large, or a large semiconductor package with a large number of pins is used, the damage of the semiconductor chip 1 will be more serious. An experiment was performed in the following manner. A semiconductor chip 1 was mounted on a 0.2-mm thick resin type circuit board 2 having flat type external connecting terminals 4 formed as shown in FIG. 3 in face-up relation (see FIG. 1) or in face-down relation (see FIG. 2). Thereafter, one surface of the circuit board 2 was sealed with a transfer mold and thereby a semiconductor package was fabricated. With the semiconductor package, a memory card, as shown in FIGS. 8 and 9, was fabricated. An external stress (such as bending force or twisting force) was applied to the memory card. Experimental results show that stress is concentrated to portions that section the flat type external connecting terminals (for example, portions of straight lines in parallel with sides of the circuit board 2 and portions of straight lines that are oblique to sides of the circuit board 2). In these portions, the circuit board 2 tends to be broken.
Therefore, a first object of the present invention is to provide a semiconductor package with high reliability.
A second object of the present invention is to provide a semiconductor package of which the damage of a semiconductor chip due to an external stress is reduced.
A third object of the present invention is to provide a semiconductor package that is compact and that has high reliability.
A fourth object of the present invention is to provide a semiconductor package that is compact and of which the damage of a semiconductor chip due to an external stress is reduced.